The present invention relates to a suction throttle valve of a compressor for use, for example, in an automotive air conditioning system and, more particularly, to a suction throttle valve of a variable displacement compressor for reducing the vibration and noise that are due to pulsation of suction refrigerant gas.
There is generally known a variable displacement compressor for use in an automotive air conditioning system and the like, which is capable of variably controlling its displacement. Such variable displacement compressor will be referred to merely as a “compressor” hereinafter. The compressor often generates noise which is due to pulsation of suction refrigerant produced when the flow rate of suction refrigerant is low. As measures against the development of such noise, some compressors have used a suction throttle valve interposed between the suction port and the suction chamber for changing open area of its suction passage in accordance with the flow rate of suction refrigerant. Japanese Patent Application Publication No. 2000-136776 (hereinafter referred to as the first reference) discloses a compressor having this type of suction throttle valve. In the compressor of the first reference, a gas passage is formed between the suction port and the suction chamber, and a valve working chamber is formed between the gas passage and the suction port. An opening control valve is vertically movably arranged in the valve working chamber. The opening control valve is urged upward by a spring accommodated in a valve chamber which is formed in the valve working chamber. The opening control valve is moved upward or downward thereby to control the open area of the gas passage in accordance with flow rate of refrigerant gas drawn into the suction chamber through the suction port. The valve chamber communicates with the suction chamber through a communication hole and the opening control valve has formed therethrough a hole.
The opening control valve of the compressor according to the first reference is adapted to move upward by the urging force of the spring thereby to reduce the opening of the gas passage when the flow rate of the suction refrigerant is low and the pressure difference between the suction port and the suction chamber becomes small, accordingly. Throttling effect of the opening control valve reduces pulsation of suction refrigerant gas caused by self-excited vibration of the suction valve and generated during operation at a low flow rate of the suction refrigerant. If a spring with a large spring constant is used with an attempt to sufficiently reduce the vibration and noise caused by pulsation of suction refrigerant gas, however, the opening control valve is not sufficiently opened during operation at a high flow rate of suction refrigerant for a higher cooling performance, inviting insufficient comfortability by cooling. This problem occurs more noticeably in a variable displacement compressor which has a wider range of refrigerant flow rate during operation.
In order to solve the above problem, Japanese Patent Application Publication No. 2005-337232 (hereinafter referred to as the second reference) proposes a compressor having a suction port and a suction chamber which are in communication with each other through a suction passage and an opening control valve having a valve working chamber which is formed in the suction passage. The valve working chamber and the suction chamber are connected through a main inlet port and a sub-inlet port which are opened to the inner wall surface of the valve working chamber. A cylindrical valve body is movably arranged in the valve working chamber for adjusting the opening of the suction passage. A valve chamber is provided in the valve working chamber on the lower side of the valve body. The valve chamber communicates with a crank chamber through a communication hole.
In the compressor of the second reference, refrigerant in the crank chamber flows into the valve chamber and the pressure difference between the valve chamber and the suction passage acts on the opening control valve. During operation of the compressor at its maximum displacement, the pressure in the crank chamber is lowered to a level that is substantially the same as that in the suction passage, so that force is not present which urges the valve body of the opening control valve in upward direction which causes the main inlet port to be closed. Therefore, when the flow rate of the refrigerant into the suction chamber through the suction port is increased, the valve body moves downward in the valve working chamber thereby to fully open the main inlet port. On the other hand, when the compressor is operating at an intermediate displacement between the maximum and minimum displacements, the pressure in the crank chamber is increased to a level that is higher than that in the suction passage, so that the valve body is urged in upward direction which causes the main inlet port to be closed and, therefore, the opening of the suction passage is restricted or throttled. In this case, damping effect against the vibration and noise development is increased in accordance with the pressure in the crank chamber.
In the compressor of the second reference, although the pressure in the crank chamber is increased particularly during operation at a low flow rate of suction refrigerant and the damping effect is increased, accordingly, the opening of the suction passage is restricted more than necessary due to the excessively high pressure in the crank chamber. Therefore, necessary flow rate of refrigerant gas is not obtained, which makes it hard for the compressor to maintain its intended performance in accordance with the operating condition of the compressor.
The present invention is directed to a suction throttle valve of a compressor which reduces vibration and noise developed by pulsation of suction refrigerant and maintains the intended performance of the compressor for the entire range of flow rate of suction refrigerant.